docs: def plot_sino(self, ax=None, element=_def.LOSImpElt, Sketch=True,
                    Ang=_def.LOSImpAng, AngUnit=_def.LOSImpAngUnit, Leg=None,
                    dL=_def.LOSMImpd, dVes=_def.TorPFilld, dLeg=_def.TorLegd,
                    ind=None, multi=False,
                    fs=None, wintit=None, draw=True, Test=True):
          """ Plot the LOS in projection space (sinogram)
  
          Plot the Rays in projection space (cf. sinograms) as points.
          Can also optionnally plot the associated :class:`~tofu.geom.Ves`
  
          Can plot the conventional projection-space (in 2D in a cross-section),
          or a 3D extrapolation of it, where the third coordinate is provided by
          the angle that the LOS makes with the cross-section plane
          (useful in case of multiple LOS with a partially tangential view)
  
          Parameters
          ----------
          Proj :      str
              Flag indicating whether to plot:
                  - 'Cross':  a classic sinogram (vessel cross-section)
                  - '3d': an extended 3D version ('3d'), with an additional angle
          ax :        None / plt.Axes
              The axes on which to plot, if None a new figure is created
          Elt :       str
              Flag indicating which elements to plot (one per capital letter):
                  * 'L': LOS
                  * 'V': Vessel
          Ang  :      str
              Flag indicating which angle to use for the impact parameter:
                  - 'xi': the angle of the line itself
                  - 'theta': its impact parameter (theta)
          AngUnit :   str
              Flag for the angle units to be displayed:
                  - 'rad': for radians
                  - 'deg': for degrees
          Sketch :    bool
              Flag indicating whether to plot a skecth with angles definitions
          dL :        dict
              Dictionary of properties for plotting the Rays points
          dV :        dict
              Dictionary of properties for plotting the vessel envelopp
          dLeg :      None / dict
              Dictionary of properties for plotting the legend
              The legend is not plotted if None
          draw :      bool
              Flag indicating whether to draw the figure
          a4 :        bool
              Flag indicating whether the figure should be a4
          Test :      bool
              Flag indicating whether the inputs shall be tested for conformity
  
          Returns
          -------
          ax :        plt.Axes
              The axes used to plot
  
          """
          if self._dsino['RefPt'] is None:
              msg = "The sinogram ref. point is not set !"
              msg += "\n  => run self.set_dsino()"
              raise Exception(msg)
          return _plot.GLOS_plot_Sino(self, Proj='Cross', ax=ax, Elt=element, Leg=Leg,
                                      Sketch=Sketch, Ang=Ang, AngUnit=AngUnit,
                                      dL=dL, dVes=dVes, dLeg=dLeg,
                                      ind=ind, fs=fs, wintit=wintit,
                                      draw=draw, Test=Test)